Pulsefree peristaltic pump and method of operating same

ABSTRACT

In a peristaltic pump in which at least two impeller rollers move codirectionally along spaced-apart portions of a flexible tube with intermittent blocking of the flow at both portions simultaneously, the part of the tube upstream of the flowblocking leading roller is placed under a pressure equaling that prevailing downstream of that roller just before the latter is lifted off the tube wall to give passage to a limited volume of the conveyed fluid. The equalizing pressure may be exerted by a plunger or another codirectionally moving roller, or by intermittently driving a third roller upstream of the trailing roller at an increased speed with reference to the flow-blocking leading roller just before the intervention of the trailing roller.

Von Casimir in] 3,826,593 [451 July 30, 1974 PULSEFREE PERISTALTIC PUMP AND METHOD OF OPERATING SAME Inventor: Wolf Von Casimir, Almeidaweg 33,

D813 Starnberg, Germany Filed: May 11, 1973 Appl. No.: 359,528

Foreign Application Priority Data May 12, 1972 Germany ..2223354 US. Cl. 417/53, 417/477 Int. Cl. F04!) 43/08, F04b 43/12, F04b 45/06 Field of Search 417/477, 475, 53

4/1973 Von Casimir.. 417/477 9/1973 Hrding 417/477 Primary Examiner-William L. Freeh Assistant Examiner-Richard E. Gluck Attorney, Agent, or Firm-Karl E. Ross; Herbert Dubno [57] ABSTRACT In a peristaltic pump in which at least two impeller rollers move codirectionally along spaced-apart portions of a flexible tube with intermittent blocking of the flow at both portions simultaneously, the part of the tube upstream of the flow-blocking leading roller is placed under a pressure equaling that prevailing downstream of that roller just before the latter is lifted off the tube wall to give passage to a limited volume of the conveyed fluid. The equalizing pressure may be exerted by a plungeror another codirectionally mov ing roller, or by intermittently driving a third roller upstream of the trailing roller at an increased speed with reference to the flow-blocking leading roller just before the intervention of the trailing roller.

10 Claims, 6 Drawing Figures PATENTEDJULBOIHM SHEET 1. 0f 3 FIG. 4

PAT ENTiuJuLsorsn SHEET 3 [1F 3 PULSEFREE PERISTALTIC PUMP AND METHOD OF OPERATING SAME l. FIELD OF THE INVENTION 2. BACKGROUND OF THE INVENTION The system of my prior patent is designed to smooth the flow of a conveyed working fluid by suppressing the pulsations which normally appear at the tube outlet as a result of variations in the delivery rate due to the peri odic re-engagement of the tube wall at'a location remote from its outlet, with. the engaging roller repeatedly sweeping a section of the tube in a succession of strokes. For this purpose,as more fully explained in that patent, my earlier system comprises a pusher member which engages the tube wall at a location downstream of the arcuate section contacted by the rollers and which is operated by the roller drive to constrict the tube with a partial blocking effect at the instant of disengagement of the leading or downstream roller from the tube. This throttling of the tube outlet prevents the rise in delivery pressure which would otherwise occur at that instant as the upstream or trailing roller intervenes to impel an additional fluid volume through the operating zone; the added pressure generated at that stage is thereby stored so as to be available in a later part of the cycle.

Though the system of my prior patent works .well in many instances, I have found that small but not always negligible pressure peaks occur therein which may be objectionable, especially with high-pressure delivery.

" 3. OBJECTS OF THE INVENTION The general object of my present invention, therefore, is to provide a further improvement in systems of this type which avoids even the minor pressure variations of a peristaltic pump as described in my prior patent.

A related object is to provide a method of operating such a pump to maintain a steady discharge pressure.

' 4. SUMMARY OF THE INVENTION In accordance with the present invention, the fluid to be conveyed is fed into the inlet end of a tube whose flexible wall is progressively deformed at an upstream point and a downstream point advancing toward the tube outlet in a series of recurrent strokes, as in the system of my prior U.S. Pat. No. 3,726,613, whereby a discharge pressureof predetermined magnitude is developed in the fluid between the downstream point and the outlet, this discharge pressure exceeding the supply pressure prevailing between the inlet and that point; by adjusting (e.g. elevating) the fluid pressure between upstream and downstream points to substantially the level of the discharge pressure, with maintenance of the adjusted pressure during the confinement period in which the tube is simultaneously obstructed at both points, I prevent the occurrence of any pressure change in the outlet upon the unblocking of the tube at the downstream point at the end of the confinement period.

Basically, there are two ways in which this adjustment of fluid pressure just ahead of the obstructed downstream point can be achieved, particularly if that fluid pressure is to be raised to a higher level. The first way involves the deformation of part of the tube wall between the two obstructed points during the confinement period; the second way is to force-feed additional fluid past the upstream point into the space between the two points immediately prior to the confinement period.

In structural terms, the development of an equalized fluid pressure between two points engaged by respective impeller means (eg roller) is achieved with theaid of pressure-control means effective in the flowblocking position of the leading impeller means. With the first mode of operation described above, the pressure-control means may comprise a thrust member engageable with the flexible tube wall at an intermediate location between the two impeller-engaged points; such a thrust member could take the form of a plunger, similar to the pusher of my prior patent but disposed upstream rather than downstream of the engagement point of the leading roller, which moves substantially at right angles to the tube wall; in the case where the leading and trailing rollers sweep the same arcuate tube section, the thrust member could be a third roller mounted on an extension of the support of the other two rollers and subjected to radial displacement by suitable control means such as a stationary cam. With the second mode of operation, the pressure-control means may comprise a feed member such as a third roller engageable with the tube wall at a location upstream of both obstruction points, this feed member being timed to operate just before the tube is blocked by the trailing roller; the sweep of that third roller, while generally synchronized with that of the other two rollers, should be faster than that of the latter rollersin order to force additional fluid into the intervening space. In that instance, the elevated pressure is generated by the compressibility of the conveyed fluid and/or by the elastic expansibility of the tube wall.

5. BRIEF DESCRIPTION OF THE DRAWING The above and other features of my invention will now be described in detail with reference to the accompanying drawing in which:

FIG. 1 is a somewhat diagrammatic view of a peristaltic pump according to the present invention;

FIG. 2 is a set of graphs serving to explain the operation of the pump of FIG. 1;

FIG. 3 is a view similar to part of FIG. 1, showing a modification;

FIG. 4 is a set of graphs relating to the operation of the pump of FIG. 3;

FIG. 5 is another set of graphs serving to explain an alternate mode of operation of the system of FIG. 1; and

, FIG. 6 shows details of a cam drive forming part of the pump of FIG. 1.

6. SPECIFIC DESCRIPTION Reference will first be made to FIG. 1 in which I have shown a peristaltic pump generally similar to that disclosed in my US. Pat. No. 3,726,613. The pump comprises a housing 1 containing a flexible and preferably elastic tube 2 with an inlet section 2a and an outlet section 2b. At 20 the tube is curved through an arc of 90 about the axis of a shaft 8; at 2d it extends over slightly more than 180 along an are centered on the axis of a shaft 7 parallel to shaft 8.

Two rollers 3 and 4 are carried on opposite ends of a supporting arm 21 secured to shaft 7 and driven counterclockwise (arrow A) with the aid of a motor 20 through a transmission 22 which correlates the speed of this arm with that of a further arm 23, keyed to shaft 8 and rotating also counterclockwise (arrow B), as well as to that of a rotating cam 16 on a shaft 9. Arm 23 supports a third roller 6 sweeping the tube section 20. In the position illustrated in FIG. 1, rollers 3 and 4 simultaneously obstruct the downstream tube portion 2d at diametrically opposite points P, Q whereas roller 6 obstructs the upstream tube portion 20 at a point R; these points of engagement move codirectionally during each cycle, i.e., during each half-turn of shaft 7, in the flow direction frominlet section'2a to outlet section 2b.

A plunger 5, guided in a stationary bearing 24, is movable by the cam 16 at right angles to a tube section 2e extending between curved portions 2c and 2d. In the mode of operation described hereinafter with reference to FIG. 2, plunger constricts the tube section 2e during a confinement period in which the flow is blocked simultaneously at points R and P; the extent of this constriction is so chosen that, without cutting off the flow through section 2e, the fluid pressure in that section is raised to the level of the discharge pressure prevailing in the outlet section 21) downstream of point P. In the alternate mode of operation to be described with reference to FIG. 5, plunger 5 may be omitted.

Though in FIG. 1 I have shown the cam 16 as hearing directly upon the stem of plunger 5, against the elastic restoring force of tube section 22 (and/or of its fluid content), I have illustrated in FIG. 6 a more elaborate camming mechanism designed to facilitate adjustment of both the stroke length of the plunger and its position of maximum constriction. For this purpose, cam 16 bears upon a lever 19 which is provided on a fulcrum and has an arcuate slot 10 receiving a hook 11 on a screw-threaded sleeve 14 which forms an adjustable linkage with a mating bolt 13 hinged at 12 to the stem of plunger 5. Relative rotation of bolt 13 and sleeve 14 varies the extreme position of plunger 5 whereas displacement of hook 11 along slot 10 modifies its stroke; the hook may be immobilized on lever 19 in a selected position by wing nut or other nonillustrated fastening means.

Reference will now be made to FIG. 2 diagrammatically showing part of the tube 2, particularly its sections 21;- 2e, in developed form. Graph (a) depicts a stage in a cycle in which the point of engagement P of roller 3 with tube portion 2d is approximately at the lower vertex of that portion, with roller 4 disengaged and with roller 6 just beginning to engage the tube portion plunger 5 is retracted, possibly with the aid of a restoring spring or the like supplementing the elasticity of the tube. The three rollers 3, 4 and 6 move at the same longitudinal speed along the tube wall, graph (b) marking the beginning of a confinement period during which the fluid is trapped in sections 2d and 2e between the downstream point P and the upstream point R. During this confinement period, as shown in graphs c) through (f), the plunger progressively constricts the tube section 2e so as to elevate the pressure therein to the level of the back pressure from a nonillustrated load obtaining in outlet section 2b. Graph (g) shows the intervention of roller 4 at point 0, this being the position represented in FIG. 1. Graph (h) indicates the end of the confinement period as the roller 3 is lifted off the tube wall to unblock the flow at point P; since the pressure on both sides of that point is now identical, this unblocking does not create any shocks or pulsations at the tube outlet. Graphs (i), (j) and (k), finally, show the retraction of plunger 5 and the disengagement of roller 6 from tube portion 20; the cycle is then repeated, with roller 4 in the lead so that its point of engagment now becomes the downstream point P.

In the system of FIG. 1 the transmission 22 controls the relative speed of rotation of shafts 7 and 8 in such a way that roller 6 performs a full revolution for each half-revolution of rollers 3 and 4; with the orbital radius of roller 6 (measured along its point remotest from shaft 8) half that of rollers 3 and 4, the two arms 21 and 23 are driven with the same angular velocity. If the number of rollers entrained by shaft 7 were increased, eg to three rollers spaced apart, the arc length of tube portion 2d could be shortened; the angular velocity of roller arm 23 would, of course, have to be correspondingly adjusted in such a case.

FIG. 5 shows a mode of operation in which arm 23, during the time of engagement of roller 6 with tube section 20, is accelerated so that point R advances at a faster rate than points P and Q. Since arm 23 must again complete. two revolutions for every revolution of arm 21, this acceleration may also be realized by doubling the length of arm 23 (thus making it equal to each half of arm 21) and driving its shaft 8 at twice the speed of shaft 7. As shown in the upper five graphs of FIG. 5, roller 6 sweeps additional fluid past the as yet unobstructed upstream point Q into tube section 2d just before the latter is blocked at both ends during a brief confinement period represented by the sixth and seventh graphs of this FIGURE. The bottom graph indicates the release of the confined fluid by the lifting of roller 3, again with no appreciable change in discharge pressure because of the pressure equalization on opposite sides of downstream point P.

In FIG. 3 I have shown a tube 2' with an inlet section 2a, an outlet section 2b and a semicircular portion 2d swept by rollers 3, 4 on a cruciform support 21' keyed to shaft 7. Support 21 also carries a pair or ancillary rollers 17 and 18 whose shafts 25, 26 are radially slidable in slots 27, 28 of the support. A stationary cam 29, which may be duplicated on opposite sides of the roller support, coacts with projecting ends of shafts 25 and 26 to urge the rollers 17 and 18 radially outwardly at the vertex of the arcuate tube portion 2d so as to constrict the tube at a location between the downstream obstruction point P and the upstream obstruction point O. This is best illustrated in FIG. 4 which shows the position of rollers 3, 4 and 17 during a fraction of a revolution of shaft 7, with the second and third graphs (counting from above) representing the confinement period. The operation of this system is thus generally similar to that described with reference to FIGS. 1 and 2.

The systems described above may be supplemented by a downstream pusher in the discharge section of the tube, similar to that described and claimed in my prior patent, as illustrated at 30 in FIG. 3.

Although the foregoing description has assumed that the discharge pressure of the conveyed fluid is to be higher than its supply pressure, it should be noted that the same-principle can be applied to a system in which the reverse is true, with the rollers driven at a rate tending to retardthe flow of the fluid due to the existing pressure differential. in that case, too, pressure equalization around a downstream obstruction point will prevent the occurrence of pulsations at the tube outlet; this can be achieved, for example, by reversing the relative speeds of rollers 6 and 3, 4 in the diagram of FIG. 5 so that the distance between the upstream roller (4) and the pressure-control roller (6) increases rather than decreases in the course of a cycle.

Moreover, the mode of operation discussed with reference to FIGS. 1 and 5 could be carried out with two rollers instead of three if, with roller 6 omitted, the angular spacing of the two co-orbital rollers 3 and 4 were made variable so that the trailing roller could be accelerated (orretarded) with reference to the leading roller during the confinement period. Thus, with rollers 3 and 4 mounted on coaxial shafts by means of separate supporting arms, trailing roller 4 might reach the central position 90 behind leading roller 3 (i.e., the position of roller 17 in FIG. 3) when the latter is in the terminal position illustrated in FIG. 1; roller 4 would then advance through 90 into the leading position of roller 3, at the normal pumping speed v, while roller 3 (trailing) swings through 270 into the central or nadir position at speed 3v. Now the speed ratio is again reversed, with roller 3 (leading) covering the final 90of its sweep at speed v whereas roller 4 (trailing) moves at three times that speed to the central position it occupied two cycles earlier. In such a system the pressure-control means according to my invention would be included in transmission 22 which would have to be designed to vary the roller speeds in the manner described.

Among the various fields of application of a pump according to this invention, the conveyance of shocksensitive substances in biochemical, medical and pharamaceutical research and industry may be particularly mentioned.

. I claim:

1. A peristalticpump comprising:

a tube provided with a flexible wall having an inlet for a fluid to be conveyed, an outlet for said fluid and 6 m a series of recurrent operating cycles by obstructing said tube at a first point progressing in the flow direction;

trailing impeller means mounted on said first support for intermittent engagement with said upstream portion for deforming the wall thereof to control the advance of said fluid toward said outlet by completely obstructing said tube at a second point progressing in the flow direction, the obstruction of the tube at said points coinciding during a confinement period of each operating cycle terminating with the unblocking of the tube at said first point, at leastone of said impeller means being effective to block the tube at any time;

drive means for rotating said supports at mutually related speeds; and pressure-control means effective in the flow-blocking position of said leading impeller means for developing between said first and second points a fluid pressure substantially equaling the pressure prevailing downstream of said first point during said period. t r

2. A pump as defined in claim 1 wherein said pressure-control means comprises a thrust memberunder the control of said drive means engageable with the tube wall at a location between said points for partially obstructing the fluid flow at said location during said confinement period.

3. A pump as defined in claim 2 wherein the said thrust member is a plunger movable substantially at right angles to the tube wall. 7

4. A pump as defined in claim 2 wherein saidupstream and downstream portions have a common center of curvature and merge into a. single arc, said supports being integral with each other, said thrust member being mounted on an extension of said supports for codirectional movement with said leading and trailing impeller means.

5. A pump as defined in claim 4 wherein said leading and trailing impeller means comprisea pair of rollers, said thrust member being a further roller provided with control means for radially displacing same during a sweep past said location.

6. A pump as defined in claim 1 wherein said pressure-controlmeans comprises a feed member under the control of said drive means engageable with the tube wall at a location upstream of said second point for forcing an increased quantity of fluid past said upstream portion in a part of each cycle immediately preceding said confinement period.

7. A pump as defined in claim 6 wherein said leading and trailing impeller means include a pair of rollers and said flexible wall forms a further arcuately curved portion at a further upstream location, said feed member comprising a third support rotatable by said drive means about the center of curvature of said further portion and a third roller on said third support engageable with said further portion during said part of each cycle for deforrning'the wall thereof at a third point progressing in the flow direction.

8. A method of delivering a continuous fluid flow substantially free from pulsations, comprising the steps of:

feeding a working fluid into the inlet of an openended tube with a flexible wall; progressively defonning the tube wall at anupstream point and at a downstream point advancing toward the tube outlet, in a series of recurrent strokes, with simultaneous obstruction of the tube at said points during a confinement period of each stroke cycle ing of the tube at said downstream point.

9. A method as defined in claim 8 wherein said adjusted pressure is created by deforming a part of the tube wall between said points during said confinement period.

10. A method as defined in claim 8 wherein said adjusted pressure is created by force-feeding additional fluid past said upstream point into the space between said points immediately prior to said confinement period. 

1. A peristaltic pump comprising: a tube provided with a flexible wall having an inlet for a fluid to be conveyed, an outlet for said fluid and an operating zone between said inlet and outlet, said operating zone including an arcuately curved upstream portion and an arcuately curved downstream portion; a first support rotatable about the center of curvature of said upstream portion; a second support rotatable codirectionally with said first support about the center of curvature of said downstream portion; leading impeller means mounted on said second support for intermittent engagement with said downstream portion for deforming the wall thereof to control the advance of said fluid toward said outlet in a series of recurrent operating cycles by obstructing said tube at a first point progressing in the flow direction; trailing impeller means mounted on said first support for intermittent engagement with said upstream portion for deforming the wall thereof to control the advance of said fluid toward said outlet by completely obstructing said tube at a second point progressing in the flow direction, the obstruction of the tube at said points coinciding during a confinement period of each operating cycle terminating with the unblocking of the tube at said first point, at least one of said impeller means being effective to block the tube at any time; drive means for rotating said supports at mutually related speeds; and pressure-control means effective in the flow-blocking position of said leading impeller means for developing between said first and second points a fluid pressure substantially equaling the pressure prevailing downstream of said first point during said period.
 2. A pump as defined in claim 1 wherein said pressure-control means comprises a thrust member under the control of said drive means engageable with the tube wall at a location between said points for partially obstructing the fluid flow at said location during said confinement period.
 3. A pump as defined in claim 2 wherein the said thrust member is a plunger movable substantially at right angles to the tube wall.
 4. A pump as defined in claim 2 wherein said upstream and downstream portions have a common center of curvature and merge into a single arc, said supports being integral with each other, said thrust member being mounted on an extension of said supports for codirectional movement with said leading and trailing impeller means.
 5. A pump as defined in claim 4 wherein said leading and trailing impeller means comprise a pair of rollers, said thrust member being a further roller provided with control means for radially displacing same during a sweep past said location.
 6. A pump as defined in claim 1 wherein said pressure-control means comprises a feed member under the control of said drive means engageable with the tube wall at a location upstream of said second point for forcing an increased quantity of fluid past said upstream portion in a part of each cycle immediately preceding said confinement period.
 7. A pump as defined in claim 6 wherein said leading and trailing impeller means include a pair of rollers and said flexible wall forms a further arcuately curved portion at a further upstream location, said feed member comprising a third support rotatable by said drive means about the center of curvature of said further portion and a third roller on said third support engageable with said further portion during said part of each cycle for deforming the wall thereof at a third point progressing in the flow direction.
 8. A method of delivering a continuous fluid flow substantially free from pulsations, comprising the steps of: feeding a working fluid into the inlet of an open-ended tube with a flexible wall; progressively deforming the tube wall at an upstream point and at a downstream point advancing toward the tube outlet, in a series of recurrent strokes, with simultaneous obstruction of the tube at said points during a confinement period of each stroke cycle whereby a discharge pressure of predetermined magnitude is developed in the fluid between said downstream point and said outlet, the tube being always obstructed at least at one of said points, said discharge pressure exceeding the supply pressure prevailing between said inlet and said downstream point; and adjusting the fluid pressure between said points to a level substantially equaling that of said discharge pressure with maintenance of the adjusted pressure during said confinement period until the unblocking of the tube at said downstream point.
 9. A method as defined in claim 8 wherein said adjusted pressure is created by deforming a part of the tube wall between said points during said confinement period.
 10. A method as defined in claim 8 wherein said adjusted pressure is created by force-feeding additional fluid past said upstream point into the space between said points immediately prior to said confinement period. 